Extractive CEMS Presentation
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INFRARED BAND CENTERS OF SOME COMMON GASES Gas NO Band Center ( m) 5.0-5.5 Wave Number (cm-1) 1800-2000 NO2 5.5-20 500-1800 SO2 8-14 700-1250 H2O 3.1, 5-5.5, 7.1-10 2.7, 5.2, 8-12 10.5 1000-1400 1800-3200 850-3700 950 CO2 NH3 GENERAL CATEGORIES OF CEMS OPACITY SINGLEPASS SYSTEMS DOUBLEPASS SYSTEMS GASEOUS EMISSION MONITORS EXTRACTIVE SYSTEMS DILUTION IN-SITU SYSTEMS REMOTE SYSTEMS IN-STACK CROSS-STACK BASIS OF CEM ANALYSIS • Extractive Dry, Wet, or Dilution • In-situ Wet basis • Dilution Wet ANALYSIS CONDITIONS • Extractive • In-Situ • Dilution • Analysis performed at controlled conditions (constant temperature and pressure) • Analysis performed at stack conditions (compensation for, or approximation of, temperature and pressure) • Analysis performed at controlled conditions CEM CALIBRATION METHODS • Extractive • Compressed gases • Internal electronic • In-Situ • Gas cell and compressed gases for point/in-situ • Internal electronic • Dilution • Compressed gases • Internal electronic ADVANTAGE OF EXTRACTIVE CEMS • Allows widest selection of analyzer technologies • Can analyze at ambient conditions for which more reference data are available • Can combine more than one analyzer (e.g., GC and FID) • Can remove interfering substances before measurement • Gas is measured on a dry basis ADVANTAGE OF EXTRACTIVE CEMS • Analyzers can be installed in an accessible, clean environment • Multi-probe capability for representative sample • Perform multiple point sampling via timesharing • Expands easily for additional sampling points • Is relative accessible for service and maintenance DISADVANTAGE OF EXTRACTIVE CEMS • Sample transport and conditioning system is expensive to install and operate and has high power requirements • Sample transport and conditioning system has potential for pluggage, leaks and condensation problems (both water and acid) • Gas conditioning is often required • May inadvertently remove substances of interest from sample gas DISADVANTAGE OF EXTRACTIVE CEMS • Condensed water and/or filter residues may need to be analyzed • Has more components and a more complicated design • Has time-lag during analysis ADVANTAGES OF IN-SITU PATH CEMS • • • • • • • Fast response time No calibration gas needed No sample transport or conditioning Simple.less expensive installation More representative gas measurement Less equipment to buy and maintain Has fewer components DISADVANTAGES OF IN-SITU PATH CEMS • Potential interference by particulate or droplets • Gas measured on wet basis,moisture content must be assumed • Sometimes cannot locate equipment downstream of sorbent injection or spray dryer systems • Analyzer is exposed to harsh operating conditions and vibrations DISADVANTAGES OF IN-SITU PATH CEMS • Limits choice of analyzers • Cannot perform a dynamic calibration when process is operating • Is relatively inaccessible for service and maintenance • Does not allow for expansion ADVANTAGES OF IN-SITU POINT CEMS • • • • • Fast response time No sample transport or conditioning Simple, less expensive installation Less equipment to buy and maintain Has few components DISADVANTAGES OF IN-SITU POINT CEMS • Representative sample difficult to obtain in some situations • Gas measured on wet basis • Vibration sensitive • Access for service and maintenance can be difficult • Limits choice of analyzer • Does not allow for expansion • Operates in a potentially harsh environment ADVANTAGES OF DILUTION CEMS • Allows wide selection of analyzers • Can analyze at ambient conditions for which more reference data is available • One dilution system can serve several analyzers • Analyzers can be installed in an accessible, clean environment • Multi-probe capability for representative sample • Heated sample lines and moisture removal system not necessary DISADVANTAGES OF DILUTION CEMS • Measurement accuracy and data precision problems may occur with highly diluted samples • Dilution system may not work on high moisture flue gas • Gas is measured on a wet basis; this may not be a problem if CO2 is used as the dilution gas • Requires additional calibration for the dilution system EXTRACTIVE SYSTEM COMPONENTS AND ACCESS. • • • • • • Sample Probe: Const./Composition Probe Blowback: Design and Frequency Sample Line: Comp./Length/Diameter Valves/Fittings: Const./Composition Pressure/Vacuum Meters: Quality Moisture Conditioning System: Refrigerated, Dilution, Capacity, Design, Construction EXTRACTIVE SYSTEM COMPONENTS AND ACCESS. • Filters: Coarse/Fine and Quality • Pumps: Capacity, type, Quality • Cabinets or Shelters: Location, Temperature Stability • System Controller: Microprocessor To Sequence/Control Automatic Functions • Electrical Support: Fuses, Circuit Breakers • Calibration Gases: Location, Injection Point, tubing Regulations, Gas Parameter COMPARISON GFC NDIR • Energy Source Nichrome Coil Nichrome Coil • Spectrometer NDIR NDIR • Reference Cell 100% CO 0% CO • Sensivity Superior due to more Inferior due to Utilization energy reaching detector of a Single Absorption and ability to utilize Multi- peak and Interference from Pass Optics CO2 & H2O • Drift • Specificity Reduced due to Higher due to two cell cancellation of light Intensity variations design Interferents absorb in CO2 & H2O interferes measure & reference due to similar absorption beams equally characteristics as CO MODEL 48C-CO Analyzer and 41CHL CO2 Analyzer • Based on EPA Reference Method (RFCA-0981-054) • Gas Filter Correlation Principal • Microprocessor control • Remote Diagnostics • No consumables GENERIC INFRARED CELL Detector Sample Filter Out Sample Cell In Reference Filter Light Source MODEL 48C Flow Selected D*etector & Pre-Amp Span CO Reactor Multi-Pass Sample Thermostated Cell Gold Optics Flow Sensor Sample Pressure Sensor Band-Pass Filter Permeation Dryer Chopper Correlation Wheel Purge Housing IR Source Chopper Motor Sample Pump Thermo Model 41C CO2 Analyzer MODEL 43C- SO2 ANALYZER • Microprocessor control • SO2 Specific • Reflective U.V. filtering • Hermetically sealed U.V. lamp • No consumables MODEL 43C-SO2 Analyzer SO2 + h Ia 1 SO2* Kf SO2* SO2 + h 2 SAMPLE IN Ia = Io[I-e-{ax(SO2)}] If Ioax(SO2) or K (SO2) SAMPLE OUT PHOTO MULTIPLIER TUBE FLASHER SUPPLY ELECTRONICS MODEL 43C- FLOW SCHEME Power Supply Signal Processing Band-pass Filter PMT Detector Photo-detector (feedback) U.V. Lamp Sample Pressure Transducer HC Kicker Span Zero Capillary Flow Transducer Span/Zero Valve Option Sample Pump Exhaust Thermo Model 43C SO2 Analyzer 15 HOW IS NO MEASURED? Chemiluminescence Technique NO + O3 NO2* + O2 NO2* NO2 + h Intensity of emitted light is proportional to NO concentration Chemiluminescent Reduction of NO2 to NO 3 NO2 + Mo 3 NO + MoO3 A molybdenum catalyst, heated to ~325oC, is used to Convert NO2 to NO LS 420 Insitu O2 Oxygen Sensor Oxygen molecules tend to flow from the reference side with the highest concentration of O2 to the sample side with the lowest O2 concentration. Within the solid electrolyte the flow of oxygen generates a voltage which is related to the concentration of O2 in the sample by the Nernst equation. %O2=20.95*10 exp(-E/C) Zirconium Oxide Electrolyte Gas Flow o 850 C - O2 - O2 E 21% O2 O2 + O2 O2 O2 O2 O O2 O2 O= O2 O2 Electrocatalytic Platinum Surface = O O2 O2 = O2 <21% O2 O2 LS420 Oxygen Analyzer • Automatic Calibration – Requires Auto Cal Unit – Calibrates in synchronism with LS710/SM8175 • Same proven in situ features – Low maintenance and high reliability – Calibration under process temp and press – Excellent accuracy and specificity – Easily integrated into CEMS package DIFFERENTIAL GAS ANALYZER CEMS BIASES BIASES Problem PRESSURE Corrective Action •Other Gases Interfere With Measurement Gas •Features of Instrumentation Produces Biases •Change Analytical Technique •Scrub Out Interfering Gas •Math Correction •Choose Analyzers Wisely •Design QA/QC Program to Address Design Features DIFFERENTIAL GAS ANALYZER CEMS BIASES BIASES Problem PRESSURE Corrective Action •Exposing Analyzers to Extreme Temperatures and Changing Barometric Pressure •Plume Downwash or Flue Gas Exhaust Into CEM Shelter Causes Systematic Error •Temperature Stabilize the Analyzer and Mathematically Compensate for Pressure Effects •Shelter or Otherwise Protect System •Filter Ambient Air DIFFERENTIAL GAS ANALYZER CEMS BIASES Problem PRESSURE Corrective Action BIASES •Incorrect Gas Values •Replace or Recertify Used During Calibration Gas Standard •Inadequate/Inconsistent •Establish Procedures Response Time That Ensure Adequate Time For Monitor Response •System Calibration •Perform Probe and Obscuring Local Biases Local Analyzer Calibration Checks In Addition System Check SOURCES OF BIASES IN DILUTION PROBES • After wet scrubbers, aerosols enter the probe and changes dynamics of dilution • Dilution probes are affected by changes in Ts, Ps, and Ms which changes dilution ratio • Calibration of dilution probes changes from calibration “gas blends” vs. “single” gases (i.e., CO2 in the blend changes Ms of the gas blend!) • Contaminated source “dilution air” effects dilution ratio ADVANTAGES OF USING DILUTION PROBES • Meets 40CFR75 emission requirements of reporting on a “wet” bases Pmr = CwAsvw • Sampling rate (~20-50 mL/min) much better than conventional extractive systems (~2-5 L/min.) • Reduces moisture of the sample gas, this not requiring “heated” sample lines to analyzer, therefore lower maintenance • Use ambient monitors which meet design and performance criteria set by EPA